linux-kernel - Re: [PATCH v9 13/15] x86/sgx: Turn on per-cgroup EPC reclamation

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Date: Thu, 22 Feb 2024 10:36:09 -0600
From: "Haitao Huang" <haitao.huang@...ux.intel.com>
To: "hpa@...or.com" <hpa@...or.com>, "tim.c.chen@...ux.intel.com"
 <tim.c.chen@...ux.intel.com>, "linux-sgx@...r.kernel.org"
 <linux-sgx@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
 "jarkko@...nel.org" <jarkko@...nel.org>, "cgroups@...r.kernel.org"
 <cgroups@...r.kernel.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, "mkoutny@...e.com" <mkoutny@...e.com>,
 "tglx@...utronix.de" <tglx@...utronix.de>, "Mehta, Sohil"
 <sohil.mehta@...el.com>, "tj@...nel.org" <tj@...nel.org>, "mingo@...hat.com"
 <mingo@...hat.com>, "bp@...en8.de" <bp@...en8.de>, "Huang, Kai"
 <kai.huang@...el.com>
Cc: "mikko.ylinen@...ux.intel.com" <mikko.ylinen@...ux.intel.com>,
 "seanjc@...gle.com" <seanjc@...gle.com>, "anakrish@...rosoft.com"
 <anakrish@...rosoft.com>, "Zhang, Bo" <zhanb@...rosoft.com>,
 "kristen@...ux.intel.com" <kristen@...ux.intel.com>, "yangjie@...rosoft.com"
 <yangjie@...rosoft.com>, "Li, Zhiquan1" <zhiquan1.li@...el.com>,
 "chrisyan@...rosoft.com" <chrisyan@...rosoft.com>
Subject: Re: [PATCH v9 13/15] x86/sgx: Turn on per-cgroup EPC reclamation

On Wed, 21 Feb 2024 05:23:00 -0600, Huang, Kai <kai.huang@...el.com> wrote:

> On Mon, 2024-02-05 at 13:06 -0800, Haitao Huang wrote:
>> From: Kristen Carlson Accardi <kristen@...ux.intel.com>
>>
>> Previous patches have implemented all infrastructure needed for
>> per-cgroup EPC page tracking and reclaiming. But all reclaimable EPC
>> pages are still tracked in the global LRU as sgx_lru_list() returns hard
>> coded reference to the global LRU.
>>
>> Change sgx_lru_list() to return the LRU of the cgroup in which the given
>> EPC page is allocated.
>>
>> This makes all EPC pages tracked in per-cgroup LRUs and the global
>> reclaimer (ksgxd) will not be able to reclaim any pages from the global
>> LRU. However, in cases of over-committing, i.e., sum of cgroup limits
>> greater than the total capacity, cgroups may never reclaim but the total
>> usage can still be near the capacity. Therefore global reclamation is
>> still needed in those cases and it should reclaim from the root cgroup.
>>
>> Modify sgx_reclaim_pages_global(), to reclaim from the root EPC cgroup
>> when cgroup is enabled, otherwise from the global LRU.
>>
>> Similarly, modify sgx_can_reclaim(), to check emptiness of LRUs of all
>> cgroups when EPC cgroup is enabled, otherwise only check the global LRU.
>>
>> With these changes, the global reclamation and per-cgroup reclamation
>> both work properly with all pages tracked in per-cgroup LRUs.
>>
>> Co-developed-by: Sean Christopherson <sean.j.christopherson@...el.com>
>> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
>> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>
>> Co-developed-by: Haitao Huang <haitao.huang@...ux.intel.com>
>> Signed-off-by: Haitao Huang <haitao.huang@...ux.intel.com>
>> ---
>> V7:
>> - Split this out from the big patch, #10 in V6. (Dave, Kai)
>> ---
>>  arch/x86/kernel/cpu/sgx/main.c | 16 +++++++++++++++-
>>  1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/cpu/sgx/main.c  
>> b/arch/x86/kernel/cpu/sgx/main.c
>> index 6b0c26cac621..d4265a390ba9 100644
>> --- a/arch/x86/kernel/cpu/sgx/main.c
>> +++ b/arch/x86/kernel/cpu/sgx/main.c
>> @@ -34,12 +34,23 @@ static struct sgx_epc_lru_list sgx_global_lru;
>>
>>  static inline struct sgx_epc_lru_list *sgx_lru_list(struct  
>> sgx_epc_page *epc_page)
>>  {
>> +#ifdef CONFIG_CGROUP_SGX_EPC
>> +	if (epc_page->epc_cg)
>> +		return &epc_page->epc_cg->lru;
>> +
>> +	/* This should not happen if kernel is configured correctly */
>> +	WARN_ON_ONCE(1);
>> +#endif
>>  	return &sgx_global_lru;
>>  }
>
> How about when EPC cgroup is enabled, but one enclave doesn't belong to  
> any EPC
> cgroup?  Is it OK to track EPC pages for these enclaves to the root EPC  
> cgroup's
> LRU list together with other enclaves belongs to the root cgroup?
>
>
> This should be a valid case, right?

There is no such case. Each page is in the root by default.

Thanks

Haitao